1. Field of the Invention
The present invention relates to an image forming apparatus, such as a color copying machine, a color laser printer, or a color LED printer, and a control method therefor, as well as a program for implementing the method and a storage medium.
2. Description of the Related Art
In the image forming apparatus of the above-mentioned type, it is necessary to cope with various environmental changes (aging of components, the amount of used toner, the number of printed sheets, etc.) to continue outputting of each of the same full-color images with the same tints of colors. To this end, whenever a predetermined time period elapses or certain conditions are satisfied, immediately before carrying out printing (immediately after reception of print data) or during printing of a plurality of pages, an operation, which is called calibration, referred to hereinafter, is executed for color density adjustment, color drift correction, etc.
Techniques related to the calibration are disclosed e.g. in Japanese Laid-Open Patent Publications (Kokai) No. H08-9178 and No. 2005-122341.
Calibration is essential for printing full-color images. However, the execution of calibration at a fixed repetition period or on the same conditions, there arises the following inconveniences:
Even during printing (during execution of printing of a plurality of sheets) in a time zone during which the printing frequency is high, calibration is executed, which compels the user who has started printing has to wait for completion of printing for a longer time period than it should be, which degrades efficiency of printing.
Further, even in the time zone during which the frequency of use of the image forming apparatus is high, the details of calibration and the time period over which calibration is executed are the same, which compels users to wait more often as the printing frequency is higher.
Further, the image forming apparatus has a sleep mode and an energy-saving mode, and there can be a case in which after returning from the sleep mode or the energy-saving mode, calibration is executed only after printing several sheets, which degrades efficiency of printing (image formation).
Further, to avoid the use of an image forming apparatus that executes a calibration operation, there have been proposed e.g. a technique of allocating print data to other image forming apparatuses. This technique, however, does not provide a solution to users who have only one image forming apparatus.